1. Field of the Invention
The present invention relates to a fiber array to be coupled to an optical element. Particularly, it relates to a fiber array, in which bare fibers of a ribbon-shaped optical fiber multi-core line are arrayed in the V-grooves of a V-shaped substrate, and a waveguide device having the fiber array sealed therein.
2. Description of the Related Art
As a result that a higher density of optical fibers disposed in an array was demanded because of an increase in charges for communications, there have been disclosed techniques on the fiber arrays of a normal pitch type, in which a plurality of optical fibers are jointed and formed into a ribbon shape. Further, there have been also disclosed techniques on the fiber arrays of a half pitch type, in which two ribbon-shaped optical fiber multi-core lines 1 and 2 of the normal pitch type are laid one over the other, and in which unjacketed bare fibers are alternately arranged in the V-grooves of a V-shaped substrate thereby to realize the desired high optical fiber density.
In these techniques, it could be said that a loss of optical signals is liable to increase in the ribbon-shaped optical fiber multi-core lines arrayed in the V-grooves of the fiber array. strictly at their outer ports. As the case may be, the bare fibers positioned on the outer sides may be broken. For a first one of these causes, the pitch of the ribbon-shaped optical fiber multi-core lines is standardized to 250 xcexcm, but is enlarged to about 100 xcexcm for the eight cores of an 8-core ribbon or to about 200 xcexcm for a 24-core ribbon due to the occurrence of errors at the jacket forming time. The magnitude of displacement of the pitch of the bare fibers from the pitch of the V-grooves is enlarged especially at the bare fibers housed in the V-grooves on the outermost sides. Therefore, a high bending force is applied to the jacket portions and further to the V-grooves. As a result, when the fibers are adhered and fixed in this state as the fiber array and are placed under a seriously changing temperature environment, the fibers are subjected at their bent portions to a severe stress thereby to cause an increase in the loss of the optical signals or to break the fibers.
Secondly, the pitch of the unjacketed bare fibers is displaced with respect to the pitch of the V-grooves, so that especially the bare fibers housed in the outermost side V-grooves are largely displaced. Therefore, in the assembling work to house the optical fibers in the V-grooves of the fiber array, the bare fibers may be brought to abut against the ends of the V-grooves to cause flaws in the outer circumferences of the optical fibers. Then, although no problem arises just after the assembly, the V-groove end portions cause the increase in the loss of the optical signals and the breakage of the optical fibers after a long period of use. Especially in the case of the fiber array in which the pitch of the V-grooves is as small as 127 xcexcm for the high density, the V-grooves are shallowed by the relation between the diameter and the pitch of the fibers to be mounted and have a narrow opening. Therefore, the problem that the bare fibers to be housed abut against the groove ends of the V-grooves is liable to become serious.
Thirdly, in order to remove the jackets of the ribbon-shaped optical fibers, a dedicated apparatus is used to apply blades vertically to the jacket portions of the optical fibers to peel off the jackets from the upper and lower portions of the optical fibers. If the upper and lower blade edges of the apparatus are inclined although should be in parallel, or if the unjacketing actions are made with the optical fiber being placed not in parallel with the upper and lower blade edges, the blade edge may contact with one optical fiber on the outer side. As a result, flaws in the outer circumference of the optical fibers are often caused, and thus the unjacketing start portion causes the increase in the loss of the optical signals and the breakage of the optical fiber.
Fourthly, moreover, the fibers on the outer sides are the more twisted with respect to the rotation, as caused at the fiber array assembling time and fixed, in a direction xcex8 z for an optical axis in a Z-direction, so that they are always subject to a high load. Fifthly, the entire ribbon is liable to slide in the widthwise direction so that a stress is applied to the bare fibers positioned on the outer sides. These fourth and fifth causes are also liable to invite the increase in the loss of the optical signals and the breakage of the optical fibers.
In the case of the fiber array of the half pitch type, moreover, the bare fibers, which are alternately arranged in one row by laminating two ribbon-shaped multi-core ribbon-shaped optical fibers vertically, are always subject to a vertically bending force. This bending force is more liable to cause the increase in the loss of the optical signals and the breakage of the optical fibers.
In the present invention according to a first aspect, there is provided a fiber array in which bare fibers of a ribbon-shaped optical fiber multi-core line are arrayed in V-grooves of a V-shaped substrate. In this fiber array, fibers for transmitting no optical signal are disposed on at least the outermost sides of the array of the bare fibers, and also disposed over at least the entire length of the fiber array. Therefore, no optical signal is transmitted to at least the outermost side fibers of the ribbon-shaped optical fiber multi-core line having the optical fibers arrayed in the V-grooves. As a result, the outermost optical fibers absorb the bending stress or the like to be applied to the remaining bare fibers. Even if the bare fibers on the outermost sides are broken in rare cases by the bending force or the like, no optical signal is transmitted. Consequently, the loss in the signals is not increased and the bare fibers on the inner side are not broken. Thus, the fiber array shows excellent stability in the long term.
Here, the phrase of xe2x80x9cfibers for transmitting no optical signalxe2x80x9d means the fibers which do not transmit the optical signals between the two ends, and covers: the fibers which are not connected with a transmission source of a receiver of the optical signals; the fibers which are connected but do not transmit the optical signals from the transmission source; and the fibers which are connected and transmit the optical signals but which are shielded (as will be called the xe2x80x9cdummy fibersxe2x80x9d). Moreover, the phrase of xe2x80x9cat least the outermost sidexe2x80x9d means the two optical fibers on the individual two sides, which are positioned on the outermost sides of the fiber arrays of the normal pitch type and the half pitch type, in which multiple fibers are arrayed in one row. Moreover, these optical fibers, i.e., the bare fibers, which are arrayed on the outermost sides in the V-grooves of the V-shaped substrate over at least the entire length of the fiber array and which do not transmit the optical signals, are constructed to include the bare fiber portions and the jackets. Further, these optical fibers are all over at least the entire length of the fiber array. Where the multi-core lines are forty or more or where the V-groove pitch is so small as to increase the bending force, it is preferred that the four optical fibers, as positioned by two individually on the outermost two sides of the fiber array of the multiple cores, are made to pass no signal.
Especially in fiber array of the half pitch type in which two multi-core ribbon-shaped optical fibers are alternately laminated in the vertical direction into one row, the bare fibers, as positioned on at least the outermost sides of the ribbon-side optical fibers arranged on the upper layer, are always subject to the vertical bending force. Therefore, the increase in the loss of the optical signals and the breakage of the fiber array can be prevented in advance by exemplifying those bare fibers by the dummy fibers for transmitting no optical signal. In the case of the fiber array of the half pitch type, on the other hand, it is preferred that the fibers, as positioned on at least the outermost sides, of the ribbon-shaped optical fibers of the upper and lower layers are exemplified by the dummy fibers. At this time, totally at least four optical fibers are the dummy fibers.
In the present invention according to a second aspect, there is provided a waveguide device, in which a fiber array having bare fibers of a ribbon-shaped optical fiber multi-core line arrayed in V-grooves of a V-shaped substrate is optically connected to a waveguide chip and is sealed in a package. In this device, fibers for transmitting no optical signal are disposed on at least the outermost sides of the array of said bare fibers, and disposed from said fiber array to at least the inner face of the package for fixing the jackets. Even in the waveguide device in which the leading ends of the bare fibers but not the jackets are fixed in the V-grooves of the fiber array and in which the jackets are fixed by the package to fix the fiber multi-core line, no optical signal is transmitted to at least the outermost side fibers. Thus, the outermost optical fibers absorb the bending stress or the like to be applied to the remaining bare fibers. Additionally, even if the bare fibers on the outermost sides are broken in rare cases by the severe vibrations or the like of the outside in which the waveguide device is placed, no optical signal has been transmitted. Therefore, the loss of the signals is not increased and so that the fiber array is not broken. Consequently, the device is excellent in a long stability.
The material for the dummy fibers is not especially limited, if it is exemplified by quartz for other optical fibers or a material having a similar shock resistance. The dummy fibers can absorb a shock even if they themselves are broken but so long as they do not come out, thereby to reduce a danger that the bending force arrives to break the inner bare fibers.